Supervolcanos
A supervolcano is a large that has had an with a (VEI) of 8, the largest possible value on the index. This means the volume of deposits for that eruption is greater than 1,000 cubic kilometers (240 cubic miles). Supervolcanoes occur when in the rises into the but is unable to break through it and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure. This can occur at (for example, ) or at zones (for example, ). Large-volume supervolcanic eruptions are also often associated with s, which can cover huge areas with lava and . These can cause long-lasting (such as the triggering of a small ) and . The of New Zealand's (about 26,500 years ago) was the world's most recent super eruption at a VEI-8 eruption. Terminology , the site of a VEI 8 eruption c. 75,000 years ago.}} .}} The origin of the term "supervolcano" is linked to an early 20th-century scientific debate about the geological history and features of the volcanic region of in the United States. In 1925, Edwin T. Hodge suggested that a very large volcano, which he named , had existed in that region. He believed that several in the Three Sisters area are the remnants of Mount Multnomah after it had been largely destroyed by violent volcanic explosions, similar to . In 1948, the possible existence of Mount Multnomah was ignored by volcanologist in his book The Ancient Volcanoes of Oregon. The book was reviewed in 1949 by another volcanologist, F. M. Byers Jr. In the review, Byers refers to Mount Multnomah as a supervolcano. Subsequent research proved that each peak of the Three Sisters was formed independently, and that Mount Multnomah did not exist. More than fifty years after Williams' book was published, the term supervolcano was popularised by the television program in 2000, to refer to eruptions that produce extremely large amounts of . The term megacaldera is sometimes used for supervolcanoes, such as the in the of and , . Eruptions that rate VEI 8 are termed "super eruptions". Though there is no well-defined minimum explosive size for a "supervolcano", there are at least two types of volcanic eruptions that have been identified as supervolcanoes: s and massive eruptions. Large igneous provinces Large igneous provinces, such as , the , , and the , are extensive regions of s on a continental scale resulting from eruptions. When created, these regions often occupy several thousand square kilometres and have volumes on the order of millions of cubic kilometers. In most cases, the lavas are normally laid down over several million years. They release large amounts of gases. The produced the Deccan Traps about 66 million years ago, coincident with the . The scientific consensus is that a impact was the cause of the extinction event, but the volcanic activity may have caused environmental stresses on extant species up to the . Additionally, the largest flood basalt event (the Siberian Traps) occurred around 250 million years ago and was coincident with the largest mass extinction in history, the , although it is unknown whether it was solely responsible for the extinction event. Such outpourings are not explosive, though s may occur. Many volcanologists consider to be a large igneous province that is currently being formed. The last major outpouring occurred in 1783–84 from the , which is approximately long. An estimated of basaltic lava was poured out during the eruption (VEI 4). The has an area of about , and the province was at least 50% larger before the and s broke away. Massive explosive eruptions Volcanic eruptions are classified using the , or VEI. It is a , which means that an increase of one in VEI number is equivalent to a tenfold increase in volume of erupted material. VEI 7 or VEI 8 eruptions are so powerful that they often form circular calderas rather than because the downward withdrawal of magma causes the overlying rock mass to collapse into the empty beneath it. Known super eruptions VEI 8 Based on incomplete statistics, at least 60 VEI 8 eruptions have been identified. VEI 7 VEI 7 eruptions, less colossal but still massive, have occurred in historical times. Four VEI 7 eruptions have occurred within the past 2000 years: 's c. 232, the of , the , and the of . * means DRE ( ). Media portrayal * featured an episode "Mystery of the Megavolcano" in September 2006 examining such eruptions in the last 100,000 years. Gallery File:San Salvador From Space.jpg|Satellite image of , and the caldera (also known as the Dark Age volcano) in the Valley of the Hammocks, site of a VEI 6–8 eruption and said to be ground zero for the , when a dark veil settled on the world. File:Taupo.Volcanic.Zone.North.Island.NZ.JPG|Volcano, lake, and caldera locations in the Taupo Volcanic Zone References Category:Earth